This invention relates to the manufacture of chlorothianthrenes and in particular to the manufacture of 2,3,7,8-tetrachlorothianthrene, in substantially pure form or as a component of a chlorothianthrene mixture. Chlorothianthrenes, especially the compound 2,3,7,8-tetrachlorothianthrene are useful as para-directing nuclear chlorination catalysts for toluene. Further details regarding chlorothianthrenes, especially 2,3,7,8-tetrachlorothianthrene and the use thereof with a Lewis acid catalyst as a chlorination catalyst may be found in copending application Ser. No. 601,219 (Case 3387), filed Aug. 1, 1975, the disclosure of which is hereby incorporated by reference. The preparation of thianthrene and various derivatives thereof including halogenated thianthrenes, are known in the art. It is known for example, to prepare such halogenated derivatives as 1-chloro, 2-chloro-, 2,7-dichloro-, 2-bromo-, 2,6-dibromo-, and the like from thianthrene directly or from other raw materials by indirect routes. The preparations of 2,3,7,8-tetrabromothianthrene by reaction of bromine and thianthrene is disclosed by Gilman et al. J Org. Chem. 23 (1958) pp. 313-314. According to the method of Gilman et al. bromine was reacted directly with thianthrene, the product treated with glacial acetic acid and the resultant suspension refluxed for 16 hours, treated with a dilute solution of sodium thiosulfate, filtered, washed with water, and dried. The resultant crude product was recrystallized twice from xylene with a final yield of 41 percent. The emphasis, in the literature directed to halogenated derivatives of thianthrene, has been toward laboratory preparations. Little or no attention has been directed to the development of practical processes for the commercial production of halogenated thianthrenes. Furthermore, the preparation of the compound 2,3,7,8-tetrachlorothianthrene, to which one aspect of the present invention is directed, is not disclosed in the prior art.
Accordingly, it is an object of the present invention to provide a process for manufacturing chlorothianthrenes that is direct and simple and readily adaptable to large scale commercial operations. It is a further object to provide a process for the manufacture of chlorothianthrene mixtures having as a major component thereof 2,3,7,8-tetrachlorothianthrene. It is a further object to provide a method of preparation of the compound 2,3,7,8-tetrachlorothianthrene. It is a still further object to provide novel and useful compositions comprising chlorothianthrene mixtures having as a major component thereof 2,3,7,8-tetrachlorothianthrene.
The thianthrene compounds prepared in accordance with the present invention are described herein in accordance with the current chemical Abstracts system whereby the numbering of ring positions is as follows: ##SPC1##